It was also before commercial fertilizer's invention. Large shipments of manure were common. In dry form, it weighed a lot less than when wet. Once water, (at sea,) hit it, it not only became heavier, but also began the process of fermentation again, of which a by-product is methane gas.
As the stuff was stored below decks, in bundles, you can see what could, (and did,) happen. Methane began to build up below decks, and the first time someone came below at night with a lantern, BOOOOOMMM ! ! !
Several ships were destroyed in this manner before it was determined just what was happening. After that, the bundles of manure were always stamped with the term, "S.H.I.T." on them, which meant to the sailors to, "Ship High In Transit." In other words, high enough off the lower decks so that any water that came into the hold would not touch this volatile cargo, and start the production of methane.
You probably did not know this true history of the word, "SHIT." Neither did I ! ! !
My pal Sal , does send me a lotta good SHIT....The Wizard finds most of the images.....there's alot of SHIT in here
(the web) !!!!!